1. Field of the Invention
The present invention relates to a substrate processing apparatus for performing various processings, such as drying, on substrates, such as semiconductor wafers, glass substrates for liquid crystal displays and glass substrates for PDPs, with a process gas which is supplied into a processing chamber together with a carrier gas.
2. Description of the Background Art
In a process of manufacturing substrates, conventionally, a substrate processing apparatus for processing substrates by supplying a process gas to the surrounding of the substrates is well known. For example, well known is a substrate processing apparatus for drying substrates by supplying IPA (isopropyl alcohol) gas to the surrounding of the substrates after being cleaned. A process gas such as IPA gas is supplied into a processing chamber by using an inert gas such as nitrogen gas as a carrier gas.
In such a substrate processing apparatus, the processing effect of drying process or the like on the substrates largely varies depending on the concentration of the process gas. For this reason, it is necessary to accurately measure the concentration of a process gas contained in gas supplied to the surrounding of the substrates. In the background-art substrate processing apparatus, the concentration of a process gas is measured by a concentration meter provided in the processing chamber or by extracting part of the gas supplied to the surrounding of the substrates.
In drying of substrates with IPA gas, it is desirable to allow the drying process on the substrates to rapidly proceed in order to prevent a drying failure such as a water mark occurring on surfaces of the substrates. Therefore, in substrate processing apparatuses of recent years, IPA gas of very high concentration is supplied into a processing chamber in some cases. In such a case where a process gas of high concentration is used, disadvantageously, there are some cases where the concentration of the process gas can not be accurately measured as the concentration of the process gas exceeds the measurement limit of a concentration meter.